Combined sequential beam switcher and duplexer using microwave circulators



Sept. 27, 1966 J. D. FACKLER 3,276,019

COMBINED SEQUENTIAL BEAM SWITCHER AND DUPLEXER USING MICROWAVECIRGULATORS Filed Feb. 11, 1964 ANTENNA ANTENNA 14 25 DIODE f DIODERECEIVER 4: SWITCH SWiTCH 3| [ll 7( TRANS- DIODE MITTER SWITCH ANTENNA ITIMNG E RING 42 45 44 COUNTER LJ E PULSE AND GEN DRIVERS M DIODE ANTENNA[31 [14 13 32 ANTENNA TRANS- MITTER DIODE SWTCH ANTENNA v 1 RECEIVERRING COUNTER PULSE GEN AND DRIVERS I NVENTOR. JOHN D FACKLER BYXWATTORNEY.

Unite States Patent 3,276,019 COMBINED SEQUENTIAL BEAM SWITCHER ANDDUPLEXER USING MICROWAVE CIRCULATORS John D. Fackler, Bedford, N.Y.,assignor to General Precision, Inc, a corporation of Delaware Filed Feb.11, 1964, Ser. No. 344,045 3 Claims. (Cl. 343-475) This inventionrelates generally to radio equipment employing successively energizedantennas each for both transmitting and receiving, and particularly to anovel arrangement for performing the dual functions of duplexing andantenna beam switching.

It is believed that the invention will have its principal application inconnection with arerial navigation systems using several successivelyenergized antennas for generating beams pointing in different directionsand/ or generating beams having different shapes. In such systems it hasbeen customary to provide a duplexer having three terminals connectedrespectively to the transmitter, the receiver and the antennas. Theantenna terminal has been connected to the various antennas throughmechanical or ferrite switches operated in the desired sequence. Such anarrangement, while satisfactory, has certain disadvantages. Ifmechanical switches are used they are subject to wear, they require aconsiderable length of time to operate, and also require a substantialamount of power for their operation. If ferrite switches are used it isfound that the field strength applied is critical, that large amounts ofpower are required to perform the switching operation at high frequency,and that the insertion loss is not constant because it is related to thefield strength.

It is a general object of the present invention to provide an improvedduplexing and beam switching arrangement.

Another object is to provide a switching system which may be operated athigh speed with very small amounts of power.

Another object is to provide a duplexer and beam switching arrangementin which the voltage standing wave ratio at the receiver is very low.

Briefly stated, the invention uses a multi-armed microwave circulatingdevice of the kind in which energy entering any arm passes through thedevice in a predetermined direction and out the next arm. Thetransmitter is connected to one arm. The various antennas are connectedto successive arms next adjacent to the transmitter while the receiveris connected to the last arm. In the path between each antenna and thecirculator there is interposed a radio frequency diode switch. Eachswitch is selectively actuatable to be either conductive or reflectiveto microwave energy. An energizing circuit controls the switches so asto render one of them conductive at a time in succession while theothers are rendered reflective. Thus energy from the transmitter passesthrough the circulator, that that antenna whose associated switch isconductive to microwave energy, is radiated, reflected, and a portionreturned to the same antenna and then through the circulator to thereceiver.

For a clearer understanding of the invention reference may be made tothe following detailed description and the accompanying drawing, inwhich:

FIGURE 1 is a block diagram of one embodiment of the invention; and

FIGURE 2 is a block diagram of another embodiment of the invention.

Referring first to FIGURE 1 the invention is shown as applied to aself-contained Doppler radar navigation system comprising a transmitter11, a receiver 12 and three antennas 13, 14 and 15. In this system it isrequired that the energy from the transmitter be passed for apredetermined time interval to the antenna 13 which radiates the energyand receives it after reflection. The reflected "ice energy is passed tothe receiver 12. During a succeeding interval, energy is transmittedfrom and reecived by the antenna 14. Finally, the antenna 15 isactivated for a similar period of time after which the cycle isrepeated. The receiver 12 utilizes the information contained in thereflected echos in a manner not here pertinent to derive informationuseful in navigation. The present invention is directed to the problemof duplexing, that is, the use of the same antenna for both transmittingand receiving, and to the problem of beam switching, that is, activatingthe three antennas sequentially. The transmitter 11 is connected to amicrowave circulator 16 having three arms 17, 18 and 19, the arm 17being connected to the transmitter. The circulator 16 is of the kind inwhich microwave energy entering the circulator by any arm is transmittedthrough the circulator in a predetermined direction as indicated by thearrow and leaves by the next adjacent arm. The circulator 16 may be anyof several commercially available models preferably one operating on theprinciple of rotation of the plane of polarization by a ferrite elementsubjected to a magnetic field.

The arm 18 of the circulator 16 which is most remote from thetransmitter 11 is connected to the receiver 12. The arm 19 is connectedto an arm 21 of a circulator 22 similar to the circulator 16. Thecirculator 22 is provided with the previously mentioned arm 21 and alsowith arms 23 and 24. The latter is connected to a radio frequency diodeswitch 25 which in turn is connected to the antenna 15. The arm 23 isconnected to an arm 26 of another similar circulator 27 having inaddition to the arm 26 two arms 28 and 29. These arms are connected toantennas 14 and 13 through radio frequency diode switches 31 and 32,respectively. All of the connections so far recited are microwavetransmission paths such as coaxial lines or waveguides.

The radio frequency diode switches 25, 31 and 32 may be any of severalcommercially available models. Each switch preferably comprises aresonant cavity such as a section of rectangular waveguide provided witha tuning post and across which is connected a diode. With the diodebiased in the forward direction so as to pass current the switch passesradio frequency energy with very little attenuation. When the diode isreversed biased, radio frequency energy is blocked and the switchreflects nearly all of the incident power. Such switches require verylittle power for their operation and may be operated at very highspeeds.

A timing pulse genera-tor 35 generates a series of narrow timing pulses36 which are applied to a waveform generating circuit 37 such as a ringcounter with suitable drivers. The latter circuit generates three seriesof rectangular voltage waves 41, 42 and 43 as shown. Each has a positivegoing portion for one-third of a cycle and a relatively negative portionfor the remaining two-thirds of each cycle. The three waveforms areout-of-phase with each other as shown. The waveforms 41, 42 and 43 areapplied through conductors 44, 45 and 46 to the diode switches 32, 31and 25, respectively. Each switch is thereby rendered conductive tomicrowave energy during the positive portion of its associated waveformand is rendered reflective to microwave energy during the negativeportion. Thus each switch is conductive one-third of the time and thevarious switches are conductive in successive time intervals.

In operation, microwave energy from the transmitter 11 passes throughthe arm 17 to the circulator 16 in the direction indicated by the arrowand leaves by the arm 19. It then travels successively through thecirculator 22 and the circulator 27 to the arm 29 and thence to thediode switch 32. When this switch is forward biased the microwave energypasses through the switch 32 to the antenna 13 and, after reflection,passes back through the antenna 3 13 and the switch 32 to the circulator27. It next travels to the arm 28 but at this time the diode switch 31is re flective so that the energy passes back through the circulator 27and through the arms 26 and 23 to the circulator 22. The diode switch 25is also reflective at this time so that the energy passes through thearms 21, 19 and 18 to the receiver 12. During the next interval thediode switch 31 is conductive so that the antenna 14 is active and inthe final interval the diode switch 25 is conductive and the antenna 15is active. The cycle is then repeated.

Considering the three circulators 16, 22 and 27 as a unit, it is notedthat there are a total of five external connection arms 17, 29, 28, 24and 18, that is, arms which are connected to external components.Finally, assuming the direction of energy flow as indicated by thearrows, the arm 29 is next adjacent to the transmitter; next insuccession are arms 28 and 24-; and finally, arm 18 is the arm mostremote from the arm 17. It is also to be noted that additional antennascould be accommodated by providing an additional circulator and diodeswitch. Referring now to FIGURE 2 there is shown an embodiment of theinvention in which the three circulators 16, 22. and 27 have beenreplaced by a single circulator 51 having five arms 52, 53, 54, 55 and56. The transmitter 11 is connected to the arm 52 while the variousantennas and diode switches are connected to the adjacent arms 53, 54and 55 respectively. The receiver is connected to the most remote arm56. The embodiment of FIGURE 2 operates in substantially the same manneras the embodiment of FIGURE 1.

In both of the embodiments illustrated phasing problems of the variousswitches are minimized. The physical distance of each switch from thecirculator is unimportant as far as the switching operation ordiscontinuities in the transmission path are concerned. It may bepreferred in some cases to make the distances from the circulator thesame in order that the phase of any leakage power may be the same. It isto be noticed that the transmission loss is the same with respect to allof the antennas because the total path length from the transmitter toeach antenna and to the receiver is the same. Additionally, it has beenfound that the described arrangement provides a very low voltagestanding wave ratio in the receiver.

Although two preferred embodiments have been described for illustrativepurposes, many modifications will occur to those skilled in the art. Itis therefore desired that the protection afforded by Letters Patent belimited only by the true scope of the appended claims.

What is claimed is:

1. A combined duplexer and switching system, compris- 111g,

microwave energy circulating means including a plurality of externalconnection arms for transmitting microwave energy entering any armthrough a portion of said means in a predetermined direction and out bythe next succeeding arm,

a source of microwave energy connected to one of said arms,

a plurality of antennas connected to successive arms next adjacent tosaid one arm,

a receiver connected to that arm most remote from said source,

a plurality of radio frequency diode switches one interposed betweeneach antenna and said circulating means,

said switches each being selectively actuable to be conductive orreflective to incident microwave energy, and

cyclically operating means for rendering each switch in successionconductive and the remainder of said switches reflective.

2. A combined duplexer and switching system, comprising,

first, second and third microwave circulators each having first, secondand third arms,

each of said circulators being for transmitting microwave energyentering by any ar-m through a portion of said circulator and out by thenext adjacent arm,

the direction of transmission being from said first to said second arms,from said second to said third arms and from said third to said firstarms, 7 v

a source of microwave energy connected to said first arm of said firstcirculator,

a receiver connected to said third arm of said first circulator,

said second arm of said first circulator being connected to said firstarm of said second circulator,

said second arm of said second circulator being connected to said firstarm of said third circulator,

three radio frequency diode switches connected to said second arm ofsaid third circulator, said third arm of said third circulator and tosaid third arm of said second circulator,

each of said switches being selectively actuable to be conductive orreflective to incident microwave energy,

three antennas, one connected to each of said switches,

and

control means for rendering each switch in succession conductive and theremaining two switches reflective to microwave energy.

3. A combined duplexer and switching system, comprising,

a microwave circulator having first, second, third, fourth and fiftharms,

said circulator being for transmitting microwave energy entering by anyarm through a portion of said circulator and out by the next adjacentarm,

the direction of transmission being from any arm to the next highernumbered arm and thence to the first,

a source of microwave energy connected to said first arm,

a receiver connected to said fifth arm,

three radio frequency diode switches, one connected to each of saidsecond, third and fourth arms,

each of said switches being selectively actuable to be either conductiveor reflective -to incident micro-wave energy,

three antennas, one connected to each of said diode switches, and

cyclically operating means for rendering said switches conductive tomicrowave energy one at a time in succession and for simultaneouslyrendering the other two switches reflective.

References Cited by the Examiner UNITED STATES PATENTS 9/1959 Heidester343876 X 5/1962 Ring 3331.1

1. A COMBINED DUPLEXER AND SWITCHING SYSTEM, COMPRISING, MICROWAVEENERGY CIRCULATING MEANS INCLUDING A PLURALITY OF EXTERNAL CONNECTIONARMS FOR TRANSMITTING MICROWAVE ENERGY ENTERING ANY ARM THROUGH APORTION OF SAID MEANS IN A PREDETERMINED DIRECTION AND OUT BY THE NEXTSUCCEEDING ARM, A SOURCE OF MICROWAVE ENERGY CONNECTED TO ONE OF SAIDARMS, A PLURALITY OF ANTENNAS CONNECTED TO SUCCESSIVE ARMS NEXT ADJACENTTO SAID ONE ARM, A RECEIVER CONNECTED TO THAT ARM MOST REMOTE FROM SAIDSOURCE, A PLURALITY OF RADIO FREQUENCE DIODE SWITCHES ONE INTERPOSEDBETWEEN EACH ANTENNA AND SAID CIRCULATING MEANS, SAID SWITCHES EACHBEING SELECTIVELY ACTUABLE TO BE CONDUCTIVE OR REFLECTIVE TO INCIDENTMICROWAVE ENERGY, AND CYCLICALLY OPERATING MEANS FOR RENDERING EACHSWITCH IN SUCCESSION CONDUCTIVE AND THE REMAINDER OF SAID SWITCHESREFLECTIVE.